Lime needs in Minnesota

What you need to know

Keep the following in mind when thinking about lime needs in Minnesota:

Liming to a pH of 6.0 to 6.5 or higher provides an ideal environment for bacteria in soils.

It also increases the supply of soil phosphorus available to plants.

Lime needs vary based on crop and geography.

The importance of lime

When needed, liming materials are major inputs for crop production enterprises in Minnesota. When soils are acid, there are many benefits from liming. Liming to a pH of 6.0 to 6.5 or higher provides an ideal environment for bacteria in soils. Some of these bacteria actively take part in the breakdown of soil organic matter. Others form nodules on the roots of legumes. With this bacterial partnership, legumes are able to utilize the nitrogen in the air and no fertilizer nitrogen is needed.

The availability of phosphorus is also affected by soil pH. So, liming to a pH of 6.0 to 6.5 also increases the supply of soil phosphorus available to plants. Most soils in Minnesota contain ample calcium (Ca) for crop growth. Liming materials are generally not used to supply Ca, but depending on source may be used to supply magnesium (Mg).

Determining the need for lime

The need for lime is not uniform across Minnesota and recommendations will vary. Analyzing a soil sample for pH and buffer pH is the only way to arrive at an accurate lime recommendation. Sample soils to a depth of 6 to 8 inches for accurate recommendations.

After the soil sample reaches the laboratory and is dried, a pH reading is taken in a mixture of equal parts of soil and water. This value is the soil pH. If the soil pH reading is less than 6.0, a buffer solution is added to the soil/water mixture and another pH reading is taken. This second reading is referred to as the buffer pH and is used to determine the amount of lime to apply. The current buffer used at the University of Minnesota is called the Sikora Buffer. The pH of the buffer itself is 7.5. When it is added to an acid soil, the pH of the buffer will drop. The change in the pH of the buffer is directly related to the amount of lime needed.

The buffer pH is not determined on soils with a soil pH of 6.0 or higher. The relative error of using the buffer is too high in this soil pH range. For these soils, standard guidelines are used to raise the soil pH to 6.5.

Lime guidelines for Minnesota are summarized in Tables 1-3. Consider the area of the state when using these suggestions (see map Figure 1).

Optimum pH varies among different crops. Minnesota crops are divided into 3 groups. These groups are as follows:

Group I. Alfalfa, alsike clover, apple, asparagus

Group II.

Annual canary seed

Barley

Birdsfoot trefoil

Buckwheat

Canola

Edible bean

Flax

Grape

Grass for seed production

Grass hay

Mustard

Millet

Oat

Pea

Raspberry

Red clover

Rye

Sorghum sudan

Soybean

Strawberry

Sugar beet

Sunflower

Sweet corn

Vegetable crops

Wheat

Group III. Potato, grass sod, blueberry, wild rice.

For mineral soils, apply lime to raise the soil pH to 6.5 if alfalfa, alsike clover, apples, or asparagus are the intended crops. For any crop in Group 2, apply lime to raise the soil pH to 6.0. The crops listed in Group 3 grow best in acid soils and no lime is needed except for potato and grass sod when the pH drops below 4.9. In these cases, we suggest an application of 2000 lb ENP/A is suggested. For potato, this apply before growing a rotation crop to minimize scab development.